The background description set out below represents a description of the background to the present invention but does not necessarily represent prior art.
Engines, e.g. those of vehicles, are equipped with a system for supply of fuel to the engine. The fuel system comprises inter alia one or more fuel tanks, various lines for transfer of fuel within the vehicle, fuel filters and valves. The fuel system for many engines comprises also injectors which inject fuel into the engine's cylinders.
The fuel system may comprise a low-pressure circuit which at a relatively low pressure pumps fuel from the one or more fuel tanks, via a pressure changer, usually a high-pressure pump, to a high-pressure circuit in which the fuel maintains a high pressure corresponding to the pressure required for its injection in the engine. A low-pressure pump in the low-pressure circuit may be for example be arranged to draw fuel from the fuel tank and then pressurise it to about 8-12 bar.
The high-pressure pump is configured to further pressurize the fuel and then feed it to one or more pressure vessels, which may take the form of a so-called common-rail unit adapted to holding the pressurised fuel for injection into all of an engine's cylinders. The fuel pressure in the common-rail unit may for example be within a range of 500 to 3000 bar. There may also be a plurality of pressure vessels, e.g. one per cylinder.
Fuel systems today usually employ a low-pressure pump which is driven mechanically by the engine and therefore imparts a pressure which depends on the speed of the engine. The capacity of the low-pressure pump, and hence also the amount of fuel supplied to the engine, are thus here substantially proportional to the engine's speed.